Aircraft commonly employ various aircraft control surfaces, such as ailerons, elevators, rudders and flaperons, which may be actuated to control the pitch, roll and yaw of the aircraft. As one example, ailerons are mounted on the wings of the aircraft and are actuated to either an up or down configuration to control lift at the respective wing. As another example, elevators are mounted on a horizontal stabilizer of the aircraft and are actuated to either an up or down configuration to control the pitch of the aircraft.
Aircraft control surfaces are actuated by a power control unit (“PCU”). For example, an aileron typically includes a bell crank that may be pushed or pulled by the PCU to effect the desired up and down motion of the aileron. For reasons of redundancy, there are typically two or three PCU's for each control surface, any of which must be capable of actuating the entire control surface. Due to the size of the PCU, conventional ailerons are cantilevered some distance away from a rear spar of the wing to allow space for the PCU. The PCU is typically installed lengthwise between the rear spar and the aileron. Therefore, use of a conventional PCU consumes limited space and adds weight.
Furthermore, due to its size and shape, the bell crank often does not fit within the aero envelope. Therefore, the bell crank must be covered with an aero blister, which also adds weight and increases excrescence drag.
High performance wings are thin. However, since bell crank-actuated ailerons are typically actuated proximate the center of the aileron, while the air loads are distributed along the entire length of the aileron, the aileron must be sufficiently stiff to resist the air loads along its entire length. The structure required to provide such stiffness significantly increases weight, particularly in thin, high performance wings.
Rotary power control units, also known as power hinges, have also been utilized to actuate aircraft control surfaces. However, rotary power control units are generally more complicated than bell crank assemblies, and do not provide distributed actuation along the length of the aircraft control surface.
Accordingly, those skilled in the art continue with research and development efforts in the field of aircraft control surface actuation.